How Does Coffee Bean Processing Shape Kenyan Flavor?
Kenyan coffee is defined less by a single tomato note than by full-bodied juiciness and bright acidity. The K72 washed method, in which parchment-covered beans ferment in water for roughly 72 hours, helps produce that clean, dense cup. Grades such as AA and AB sorted by bean size do not automatically signal better flavor, since the Coffee Board auction judges lots mainly by cupping quality.
SL28 and SL34 varieties grow at altitudes between 1,500 and 2,100 meters, with two harvests a year. Pickers patrol the trees about seven times to take only ripe cherries. Because climate and soil shift from season to season, the acidity and specific fruit notes fluctuate across harvests even when the juicy structure stays consistent.
Kenyan coffee has always been famous for its full-bodied juiciness and bright acidity, but many people mistakenly believe that only a small tomato flavor represents Kenyan flavor. This article comprehensively sorts out the core knowledge of Kenyan coffee, from the producing environment, auction trading system, and green bean grading, to the characteristics of the SL28 and SL34 varieties, the K72 washed processing method, and the six major producing regions such as Nyeri and Kirinyaga. At the same time, Front Street Coffee uses two Kenyan AB beans for roasting, cupping, and brewing comparisons to help you understand the flavor differences brought by different altitudes and producing regions, as well as grinding and brewing suggestions for Kenyan coffee.
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When Kenyan coffee is mentioned, many people's first reaction is a distinct small tomato flavor, and they even feel that beans lacking this tomato flavor cannot be considered authentic Kenyan. Front Street does not agree with this single way of judging. The original flavor foundation of the Kenyan producing region is actually a thick, juicy mouthfeel.
Plant growth cannot be separated from soil and environment, and coffee trees are the same. Changes in the climate and soil conditions of a producing region will cause fluctuations in the flavor of coffee beans in each harvest season. Front Street has cupped many Kenyan coffees in recent months and found that no matter which producing region they come from, they all have a full-bodied juiciness, but the acidity and specific flavors still differ.
Kenya is a well-known coffee-producing country in East Africa and an important source of specialty coffee worldwide. Kenyan coffee is full in flavor and highly recognizable, and its trading system is also quite refined. Grades such as AA or AB, which are divided by bean size, cannot directly be equated with flavor quality; the Coffee Board auction lots mainly use cupping flavor as the basis, and the auction prices of specialty Kenyan coffee have long remained high. Kenyan coffee is mostly grown at altitudes between 1,500 and 2,100 meters, with two harvest periods a year. In order to ensure that only ripe cherries are picked, people need to patrol repeatedly among the trees, about seven times back and forth.
Kenya has two coffee sales systems: one is the auction held at the Nairobi Coffee Exchange (the central auction system), through which about 85% of coffee beans are traded; the other is direct trade, often called the "second window," through which only about 15% of coffee beans circulate.
The Nairobi Coffee Exchange is the core platform for Kenyan coffee auctions. Auctions are currently held once every two weeks, with bidding fixed on Tuesdays. Twelve days before the auction begins, marketing agents send green bean samples to the NCE for display, giving buyers ample time to select items and do cupping. Each auction usually has hundreds of lots, sometimes even more than a thousand, and the whole process lasts almost all day, starting at 9:30 in the morning and continuing until four or five in the afternoon without a break. Inside the venue, dozens of buyers bury themselves in green bean catalogs, bidding while recording the transaction price of each green bean.
The current Kenyan coffee industry chain is roughly as follows: after coffee farmers harvest the cherries, they send them to washing stations, where preliminary density grading is first done, and then they are handed over to marketing agents. At the washing station, coffee beans are graded by screen size into the familiar AA, AB, PB, C, and so on. The green bean samples are then transferred to the NCE to participate in the auction and provide a catalog. At the auction, buyers bid on the green beans that meet their needs, and finally they are exported abroad. It can be seen that the NCE is in the middle of the entire industry chain, providing an auction platform.
Kenyan coffee bean grades AA Plus (AA+): AA grade with particularly excellent cup quality (flavor, mouthfeel). AA screen size: 17-18. AB screen size: 15-16, accounting for most of the production. C screen size: smaller than AB. TT: lighter beans blown out from AA and AB grade beans by an airflow separator. T: lighter beans blown out from C grade beans by an airflow separator. E Elephant Bean: a large mutant bean formed by two beans joined together, also called elephant ear. PB Peaberry: classified by appearance, unrelated to flavor or weight. Kenyan coffee producing regions mainly consist of six major producing regions including: Thika, Kirinyaga, Mt. Kenya West, Nyeri, Kiambu, and Muranga. The harvest periods of the six major producing regions are all from October to December (main crop season) and June to August (secondary crop season) of the year. Among them, Nyeri and Kirinyaga are the most famous.
Nyeri is located in the high mountain area near Mount Kenya and is an important producing area for Kenya's specialty-grade coffee, with an average altitude of more than 1,500 meters. Many high-quality Kenyan coffees come from here. Nyeri is high enough in altitude and is also east of the Aberdare Mountains, while being located on the promontory between Mount Kenya and the main mountain. The high terrain and fertile soil have made Nyeri an important central town for Kenyan coffee, and related industrial facilities are also relatively developed.
The Kirinyaga producing region is located on the slopes of Mount Kenya, at an altitude of about 1,300 to 1,900 meters, adjacent to the Nyeri producing region. It is world-famous for coffee with strong flavor, rich layers, and a solid mouthfeel, and together with the Nyeri producing region, it is recognized as one of the two currently best producing regions in Kenya.
Coffee bean varieties
SL28 is a single variety selected in 1935 from a drought-resistant population of the Tanganyika variety. SL28 is suitable for cultivation at medium to high altitudes and has drought resistance, but it is very sensitive to the main coffee diseases. SL28 beans resemble the Bourbon variety, round-bodied and thick. In recent years, genetic testing has also confirmed that SL28 belongs to the Bourbon genetic group.
SL34 was first selected in the late 1930s at the Scott Agricultural Laboratories in Kenya. SL34 was selected from a tree on the Kabete Loresho estate in Kenya, and this tree was called "French Mission." SL34 beans resemble the Typica variety. Front Street selected beans from Kenyan coffee that resemble Typica in appearance, with elongated bodies, oval shape, and a relatively flat look from the side. In recent years, genetic testing has shown that SL34 is related to the Typica genome.
Coffee bean processing methods
Generally speaking, the washed processing method for coffee beans is to first remove the peel and pulp of the coffee cherry, leaving only a thin layer of mucilage for washing fermentation for 24-48 hours, and finally drying with a machine or under the sun. However, the Kenyan-style washed processing is somewhat different, and the entire fermentation process reaches 72 hours.
Kenyan-style washed processing adopts a repeated cycle method of fermenting and then washing. On the day of harvest, the highest-quality cherries are selected, depulped, and fermented for 24 hours, then washed with clean river water after 24 hours. Next, they are fermented again with clean river water for 24 hours, then washed again, repeating this cycle 3 times to reach 72 hours, so it is called the Kenyan-style 72-hour fermentation washed processing method, or K72 for short. Front Street believes that this processing method allows the coffee beans to ferment for a long time at low temperatures, enabling the beans to present a brighter, cleaner yet fuller flavor.
Next, FrontStreet Coffee compares coffee beans from two producing regions through roasting, cupping, and brewing to see what differences there are in flavor.
FrontStreet Coffee — Kenya Gathaithi Cooperative AB coffee beans
Producing region: Kenya Nyeri Gathaithi Cooperative
Washing station: Gathaithi Washing Station
Altitude: 1825m
Variety: SL28&SL34
Processing method: K72 washed
FrontStreet Coffee — Kenya Mugaya AB coffee beans
Producing region: Kenya Mugaya Washing Station
Altitude: 1400m
Variety: SL28&SL34
Processing method: K72 washed
Harvest season: 2020
FrontStreet Coffee roasting record Gathaithi coffee bean roasting: Front Street's roaster used a Yangjia 800N semi-direct fire, with a charge weight of 480g. The beans were put in when the drum temperature reached 165°C, the damper was set to 3, and the gas was set to 120. Turning point: 1'28". When the temperature rose to 140°C, the damper was set to 4. Roasted to 6'00'', temperature 153°C, the bean surface turned yellow, the grassy smell completely disappeared, and dehydration was complete. When ugly wrinkles and dark spots appear on the bean surface, and the toast smell clearly turns into coffee aroma, this can be defined as the prelude to first crack. At this time, it is necessary to listen clearly to the sound of the first crack. First crack began at 9'17'', the damper remained unchanged, the gas was reduced to 90 at 188°C, first crack development time was 2'00'', and the beans were dropped at 193.5°C.
Mugaya coffee bean roasting: Front Street's roaster used a Yangjia 800N semi-direct fire, with a charge weight of 480g. The beans were put in when the drum temperature reached 160°C, the damper was set to 3, and the gas was set to 120. Turning point: 1'28". When the temperature rose to 130°C, the damper was set to 4. Roasted to 6'00'', temperature 154.6°C, the bean surface turned yellow, the grassy smell completely disappeared, and dehydration was complete. When ugly wrinkles and dark spots appear on the bean surface, and the toast smell clearly turns into coffee aroma, this can be defined as the prelude to first crack. At this time, it is necessary to listen clearly to the sound of the first crack. First crack began at 9'28'', the damper remained unchanged, first crack development time was 2'20'', and the beans were dropped at 193.8°C.
FrontStreet Coffee cupping report
FrontStreet Coffee conducts cupping within 8-24 hours after the sample coffee beans are roasted. The cupping bowls generally used by FrontStreet Coffee baristas have a capacity of 200ml ceramic bowls. The water temperature used for cupping is 94°C. The grind size is controlled so that the passing rate through a No. 20 standard sieve (0.85 mm) is 70%-75%. Ratio: 11 grams of coffee powder plus 200 milliliters of hot water, that is, 1:18.18, so that the extracted concentration is exactly within the golden cup range of 1.15%-1.35%, and the steeping time is 4 minutes.
Gathaithi coffee bean dry aroma: citrus; wet aroma: plum; flavor: citrus, plum, berries, honey, grape, tea-like. Mugaya coffee bean dry aroma: berries; wet aroma: caramel; flavor: smoked plum, plum, grape, caramel, nuts. From cupping the two beans, we can notice that the higher-altitude Gathaithi coffee beans have richer acidity, because the large temperature difference between day and night caused by higher altitude makes the coffee trees grow more slowly, giving more time for the coffee flavor to form.
FrontStreet Coffee brewing insights
Dripper: V60 #01 Water temperature: 90°C Dose: 15g Coffee-to-water ratio: 1:16 Grind size: medium-fine grind (sifting to 77% through a No. 20 sieve)
Front Street brewing method: first rinse the filter paper and preheat the dripper and coffee pot. Use 30 grams of water for blooming for 30 seconds, then pour in a small stream in circles until 130 grams, at which point split the pour. When the water level is about to expose the coffee bed, continue pouring until 240 grams and stop pouring. When the water level is about to expose the coffee bed, remove the dripper. (Start timing from the beginning of blooming.) The extraction time is 2 minutes.
The above content is compiled by CoffeeHunters, a coffee news website.
